Tailgate lifts for vehicles are a well-recognized and well-developed art. They are customarily mounted to the rear end of a truck, often in place of its tailgate. Their function is to provide a platform that can be raised and lowered. Articles to be loaded are placed on the platform at a lower elevation. The platform is raised to the level of the truck. The article can then be moved onto the truckbed. Unloading articles is the reverse procedure. The energy to raise the articles is provided by some motive means, usually a hydraulic piston-cylinder rod assembly.
Lifts are known whose platforms are tilted up against the truck frame to act as a tailgate. Others are known which fold beneath the truckbed.
Because of the physical structure that is involved, the platform level in its lowermost position is invariably above the adjacent round level. To facilitate placing the articles on the platform and removing them, a ramp is usually mounted to the edge of the platform. Then a hand truck can more conveniently be run up to or down from the platform.
However such ramps are usually quite short and it can be an inconvenience to go too quickly from an upper level to a lower level or from a lower lever to an upper level in a short distance. Also, some loads are not amenable to this kind of handling.
A more convenient platform loading or platform unloading technique is to have the platform tilt itself. Platform tilting is in fact known, but is not common in the United States. One reason that platform tilting has not become popular is because a lift that provides it must function in two different modes (lift/lower, and tilt). It is necessary not only to provide means to power the lift in both modes, but to assure that the modes will not become confused.
Further, because trucks park where they must, it is not acceptable for a lift to be operable in the tilt mode only at some single defined elevation of the platform. The elevation relative to the truck is ranted and constant. But the elevation of the pavement or of a loading dock may vary relative to the platform, and usually will.
It is an object of this invention to provide a tailgate lift that can operate in either mode at any level, but never in both modes simultaneously.
Tailgate lifts, while not inherently dangerous, still function to lift, lower and transfer appreciable loads, and are operated by personnel having various degrees of ability and awareness. For this reason the mechanism must be simple, rugged, and reliable. The more complication there is, the more there is to go wrong. Complicated mechanisms are one of the reasons why tilting tailgate mechanisms have not achieved the acceptance which the convenience they provide should justify.
Accordingly, another object of this invention is to provide a tiltable lift with suitable exclusivity of function and simplicity of construction.
This invention also is intended to offer additional advantages over known tilting tailgate lifts. For example, known lifts generally use an upper platform pivot around which the tilting action occurs. When this is the situation, the lower platform pivot must scrape along the ground and the resulting friction forces can even frustrate the tilting movement, especially if the platform is heavily loaded. In the instant invention, the platform tilts around the bottom platform pivot, and there is no frictional reaction with the ground.
As a further example, in known tiltable lifts which are powered by hydraulic piston/cylinder assemblies, a hydraulic leak not only enables the platform to lower, but also enables it to tilt. This is not the situation in the instant invention. In the instant invention a hydraulic leak will permit the platform to lower, but not to tilt. Tilting of the instant system requires a positive control and drive. Thus, a hydraulic leak cannot result in a tilt of the platform.
As still another advantage, because the tilting action requires a positive control, namely the positive drive of a linkage, the rate of tilting can both be controlled and limited. Tilting need never be abrupt.